Data processing apparatus and data processing method

ABSTRACT

The present invention reduces an uneven color of a color having two or more colors of inks, the uneven color occurring due to manufacturing variations of ink ejection nozzles and so on. Each of a plurality of correction tables that is assigned to each predetermined number of nozzles that are used for printing on a common region in the print medium, of a plurality of nozzle arrays formed on a print head, each of the nozzle arrays ejecting a plurality of inks including a first ink and a second ink whose color is different from the color of the first ink, is generated on the basis of at least an ink ejection property of nozzles ejecting the first and second inks.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data processing apparatus and dataprocessing method that are used for image processing.

2. Description of the Related Art

A plurality of ink ejection nozzles, each being designed so as to ejectthe same ink volume, actually eject different ink volumes due tomanufacturing variations. Accordingly, if the plurality of ejectionnozzles are used to form an image on a print medium with the same numberof dots, an even density may occur due to, for example, manufacturingvariations.

In order to solve the problem of such an uneven density, Japanese PatentLaid-Open No. H10-013674 (1998) discloses a head-shading technique inwhich information on an ink volume ejected from each of ink ejectionnozzles is obtained and on the basis of this information the number ofprint dots is changed.

The head-shading technique can solve the problem of an uneven density ineach ink color by changing the number of print dots, but cannot solvethe problem of an uneven color of a color formed by two or more inkcolors due to an ink ejection volume of each of the ink ejectionnozzles.

SUMMARY OF THE INVENTION

The present invention has an objective to reduce an uneven color of acolor formed by two or more ink colors due to manufacturing variationsof ink ejection nozzles and so on.

A data processing apparatus according to the present invention performscolor correction processing on a color signal of each pixel of imagedata to be printed on a print medium using a print head, the colorsignal having a plurality of elements in a predetermined color space.The data processing apparatus includes a table generation unitconfigured to generate a plurality of correction tables assigned to eachnozzle or each of a predetermined number of nozzles that are used forprinting on a common region in the print medium in a plurality of nozzlearrays, respectively, the plurality of nozzle arrays being formed on theprint head and ejecting a plurality of inks including a first ink and asecond ink having a different color from the first ink, wherein, thetable generation unit generates each of the plurality of correctiontables on the basis of an ink ejection property of nozzles that eject atleast the first and second inks.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an ink jet printer according to oneembodiment of the present invention;

FIG. 2 is a block diagram illustrating a configuration of a print systemaccording to one embodiment of the present invention;

FIGS. 3A to 3C are diagrams illustrating occurrence of a color shiftwhen a color is formed by overlapping a plurality of different inks;

FIGS. 4A to 4D are block diagrams illustrating configurations of animage processing unit in an ink jet printer according to a firstembodiment and its variations of the present invention;

FIGS. 5A and 5B are flow charts, illustrating processing to generateparameters of a table used in an MCS processing section 404 illustratedin FIG. 4A and processing by the MCS processing section 404 using thetable in image processing for generating print data, respectively;

FIGS. 6A and 6B are diagrams illustrating printing of an image formeasurement in Step S502 in FIG. 5A;

FIGS. 7A and 7B are diagrams illustrating an image printed in Step S508in FIG. 5B;

FIG. 8 is a diagram illustrating another example of processing togenerate a table parameter of the MCS processing section;

FIGS. 9A and 9B are flow charts, illustrating processing of a tableparameter of an MCS processing section and processing by the MCSprocessing section, respectively, according to a first variation of thefirst embodiment;

FIGS. 10A and 10B are diagrams illustrating an MCS processing flowaccording to a second variation;

FIGS. 11A and 11B are diagrams illustrating an example of a print imageduring an MCS processing parameter generation process according to athird variation;

FIG. 12 is a diagram illustrating a patch color suitable for MCSprocessing;

FIG. 13 is a diagram illustrating an example in which a color on thesurface of a color cube is estimated;

FIG. 14 is a diagram illustrating an example in which a color inside acolor cube is estimated;

FIG. 15 is a diagram illustrating an example of a patch color thatenables color information to be more accurately and efficientlyobtained;

FIG. 16 is a diagram illustrating an example in which a patch colorsuitable for MCS processing is printed on a print medium;

FIG. 17 is a diagram illustrating an example in which a patch color thatenables color information to be more accurately and efficiently obtainedis printed on a print medium;

FIG. 18 is a diagram illustrating a relationship between the number ofejection for each ejection port and a density of ink;

FIGS. 19A to 19C are block diagrams illustrating configurations of animage processing unit to generate print data according to a secondembodiment and its variations of the present invention;

FIGS. 20A and 20B are flow charts, illustrating processing to generateparameters for a table used in an ink color conversion processing & MCSprocessing section 2104 in FIG. 19A and processing by the ink colorconversion processing & MCS processing section 2104 using this table;

FIG. 21 is a schematic diagram showing the print heads 101 to 104according to one embodiment of the present invention; and

FIGS. 22A to 22C are views for illustrating a positional errorcorrection of an ejection substrate of a print head according to oneembodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described with reference todrawings.

FIG. 1 is a schematic diagram illustrating an ink jet printer accordingto one embodiment of the present invention. As illustrated in FIG. 1, aprinter 100 has print heads 101 to 104 on a frame composing aconstructional material of the printer. The print heads 101 to 104 arefull-line type print heads, each having a plurality of nozzles forejecting black (K), cyan (C), magenta (M), or yellow (Y) ink arrangedover a width of a print paper 106. A resolution of nozzle arrangement ofnozzle array of each color is 1200 dpi.

FIG. 21 is a schematic diagram showing the print heads 101 to 104according to one embodiment of the present invention. Each of the printheads 101 to 104 has a plurality of ejection substrates which arearranged in order in the nozzle arrangement direction. The end portionof respective ejection substrates overlaps the end portion of theadjacent ejection substrate. The respective substrates have four nozzlearrays. For example, the print head 101 has ejection substrates 1011 to1015 and the ejection substrates are arranged so as to be shifted in thenozzle arrangement direction as shown in FIG. 11. Further, the ejectionsubstrate 1011 in the print head 101, the ejection substrate 1021 in theprint head 102, the ejection substrate 1031 in the print head 103 andthe ejection substrate 1041 in the print head 104 are arrayed in adirection (conveying direction) crossing the nozzle arrangementdirection.

The print paper 106 as a print medium is conveyed in a direction of anarrow illustrated in FIG. 1 as a conveying roller 105 (and a roller thatis not illustrated) is rotating by a driving force of a motor (notillustrated). While the print paper 106 is being conveyed, the pluralityof nozzles of each of the print heads 101 to 104 eject ink according toprint data thereby to sequentially print one raster of imagecorresponding to a nozzle array of each of the print heads. By repeatingsuch an ink ejection operation from each of the print heads to a printpaper that is being conveyed, one page of images, for example, can beprinted. A printing apparatus that the present invention can be appliedto is not limited to the full-line type apparatus as described above. Itis obvious form the above description that the present invention can beapplied to, for example, a serial-type printing apparatus in whichprinting is performed by scanning a print head in a directionintersecting with a conveying direction of the print paper.

FIG. 2 is a block diagram illustrating a configuration of a print systemaccording to one embodiment of the present invention. As illustrated inFIG. 2, this print system is composed of the printer 100 illustrated inFIG. 1 and a personal computer (PC) 300 as a host apparatus.

The host PC 300 is composed mainly of the following components. A CPU301 performs processing according to programs stored in an HDD 303 and aRAM 302. The RAM 302 is a volatile storage and temporarily stores aprogram and data. The HDD 303 is a nonvolatile storage and similarlystores a program and data. A data transfer interface (I/F) 304 controlssending and receiving data between the host PC 300 and printer 100. As aconnection for sending and receiving data, USB, IEEE1394, LAN and so oncan be used. A keyboard and mouse I/F 305 is an I/F that controls ahuman interface device (HID) such as a keyboard and a mouse, and a usercan perform inputting through this I/F. A display I/F 306 controlsdisplaying on a display (not illustrated).

The printer is composed mainly of the following components. A CPU 311performs processing of each embodiment, which will be described withreference to FIG. 4A and its subsequent Figs., according to programsstored in a ROM 313 and a RAM 312. The RAM 312 is a volatile storage andtemporarily stores a program and data. The ROM 313 is a nonvolatilestorage and can store a program and table data generated in processingof each embodiment, which will be described with reference to FIG. 4Aand its subsequent Figs.

A data transfer I/F 314 controls sending and receiving data between theprinter 100 and PC 300. A head controller 315 supplies print data toeach of the print heads 101 to 104 illustrated in FIG. 1 and controls anejection operation of the print heads. Specifically, the head controller315 can read a control parameter and print data from a predeterminedaddress from the RAM 312. Then, when CPU 311 writes the controlparameter and print data in the predetermined address of the RAM 312,the head controller 315 initiates processing and print heads eject ink.An image processing accelerator 316 is composed of hardware and performsimage processing faster than the CPU 311. Specifically, the imageprocessing accelerator 316 can read a parameter and data necessary forimage processing from a predetermined address of the RAM 312. Then, whenthe CPU 311 writes the parameter and data in the predetermined addressof the RAM 312, the image processing accelerator 316 is initiated toperform a predetermined image processing. According to the presentembodiment, processing to generate a parameter of a table used in theMCS processing section will be performed by software in the CPU 311,which will be described with reference to FIG. 4A and its subsequentFigs. Meanwhile, image processing for printing including processing inthe MCS processing section is performed by hardware processing in theimage processing accelerator 316. The image processing accelerator 316is not necessarily an essential component, and it is obvious that bothof the table parameter generation processing and image processing may beperformed by only processing by the CPU 311, depending on thespecification of a printer.

Several embodiments for reducing a color shift caused by ink ejectionvolume variations among a plurality of nozzles when a plurality of typesof inks are used to print an image in the printing system describedabove, will be described below. In a conventional head shading techniquein which each of data formed by a plurality of different types of inksis individually corrected, if the plurality of different types of inksare overlapped to express a color, a color shift that the expressedcolor is different from the intended color may occur.

FIGS. 3A to 3C are diagrams illustrating this color shift. Here, anexplanation will be made with reference to a portion of nozzles in theprint heads 102 and 103 illustrated in FIG. 21. In FIG. 3A, 102indicates the print head that ejects a cyan ink and 103 indicates theprint head that ejects a magenta ink. In order to simplify descriptionand illustration, FIG. 3A illustrates only eight nozzles of a pluralityof nozzles of each of the print heads, and illustrates only two printheads by way of example in order to describe a color shift that mayoccur when blue is printed by cyan and magenta inks.

In FIG. 3A, eight nozzles 10211, 10221 of the cyan ink print head 102all have a normal ejection volume. Meanwhile, four nozzles 10311 on theleft of eight nozzles of the magenta print head 103 in FIG. 3A have anormal ejection volume, but four nozzles 10321 on the right of them inFIG. 3A all have a larger ejection volume than the normal ejectionvolume. The four nozzles on the right of the magenta ink print head 103illustrated in FIG. 3 all are illustrated to have a larger size than thefour nozzles on the left, which is for easier understanding of thedifference of their ejection volumes, not for illustrating the actualdifference of their nozzle sizes.

When a print head having such an ejection volume characteristic is used,if image data is corrected by a conventional head shading, binary data(dot data) corresponding to a nozzle can be eventually obtained. Ifthese cyan and magenta dot data were individually printed on the printpaper 106 without overlapping, they would be printed as illustrated inFIG. 3B. FIG. 3B illustrates dots printed in such a way that a solidimage, that is, image data in which both of cyan and magenta are 100%duty, is subjected to head shading processing, and then is subjected tobinarization processing, and printed.

FIG. 3B illustrates cyan dot data 10611, 10621 corresponding to thenozzles of the cyan ink print head 102 and magenta dot data 10612, 10622corresponding to the nozzles of the magenta ink print head 103. Dot data10622 in a region corresponding to the four nozzles 10321 with a largerejection volume of magenta ink, image data of the corresponding regionis corrected by head shading, thereby reducing the number of dot data.FIG. 3 illustrates an example in which an area of a dot formed by inkejected from magenta ink nozzles 10321 with a larger ejection volume istwice as large as an area of a dot formed by ink with a normal ejectionvolume. In this case, the number of dot data is reduced by half (fromfour dots to two dots) by correction of head shading. The number of dotdata is reduced by half when an area of a dot doubles in order tosimplify description. Needless to say, the number of dot data isactually set so that the increase (decrease) of density caused byincrease (decrease) of an area of a dot due to ink ejection volumevariations can be suppressed and as a result a normal density can beobtained.

FIG. 3C illustrates an example in which, on the basis of dot dataobtained as described above, cyan and magenta inks are ejected from therespective print heads on the print paper 106 thereby to print a blueimage. In a region on the left in FIG. 3C of the print paper 106,standard-size blue dots 10613, which are formed by overlapping of cyanand magenta inks, are printed. Meanwhile, in a region on the right inFIG. 3C corresponding to four nozzles 10321 with a larger ejectionvolume of a magenta ink, the following dots are printed: standard-sizecyan dots 10623, as well as dots, each being composed of a blue area10624 formed by overlapping cyan and magenta inks and a magenta area10625 surrounding the blue area 10624.

In this way, the region for printing a blue (solid image) on the rightin FIG. 3C corresponding to magenta nozzles 10321 with a larger ejectionvolume is composed of the following three types of dots or areas:

two standard-size cyan areas (dots) 10623

two standard-size blue areas 10624, each of which is a standard-sizecyan dot formed within a magenta dot larger than the standard size

two magenta areas 10625, each of which surrounds the standard-size bluearea 10624

Here, as described above, in a conventional head shading method, each ofcyan image data and magenta image data is individually corrected toadjust the number of dots of each of cyan and magenta. The result is anarea of two cyan areas (dots) 10623=an area of two blue areas 10624=anarea of two magenta areas 10625. In this case, it is assumed that acolor on the whole observed by the optical absorption property of thecyan areas 10623 and the optical absorption property of the magentaareas 10625 is the same as a color observed by the optical absorptionproperty of the blue areas 10624. At this time, this whole region hasthe same color of the blue areas 10624.

However, when an area such as the blue area 10624 is formed byoverlapping of a plurality of different types of inks, a color observedby the optical absorption property of the area is often different from acolor observed by combining the optical absorption properties of therespective areas of the plurality of inks. As a result, a color in thewhole region shifts from an intended standard color, and therefore ablue image on the left half region in FIG. 3C appears to have adifferent color from the color of a blue image on the right half regionin FIG. 3C in the print paper 106.

Also in a multiple-valued printing apparatus in which the size of dotsare variable, such as a quaternary printing apparatus that performsprinting with three sizes of dots, that is large, medium and small dots,the dimensions of dots of the respective sizes often vary due to inkejection volume variations among nozzles. Also in this case, even ifcorrection by conventional head shading is performed, a color shift mayhappen due to the same reason as above. Therefore, the present inventioncan also be applied to a binary printing apparatus, as well as amulti-valued printing apparatus such as ternary and more-valued printingapparatuses.

In each embodiment of the present invention that will be describedbelow, a correction table to be used in an image processing process forreducing the aforementioned color shift is formed by subjecting imagedata composed of a plurality of sets of color signals beforequantization to correction processing.

First Embodiment

FIG. 4A is a block diagram illustrating a configuration of an imageprocessing unit of an inkjet printer according to a first embodiment ofthe present invention. That is, in the present embodiment, the imageprocessing unit is composed of components for control of the printer 100illustrated in FIG. 2 and image processing. It should be appreciatedthat application of the present invention is not limited to thisconfiguration. For example, the image processing unit may be configuredin the PC 300 illustrated in FIG. 2, or part of the image processingunit may be configured in the PC 300 and the other part thereof may beconfigured in the printer 100.

As illustrated in FIG. 4A, an input unit 401 inputs image data sent fromthe host PC 300 and passes the data to an image processing unit 402. Theimage processing unit 402 processes a color signal in a process ofconverting the input image data to a signal that can be printed by theprint head. This image processing unit 402 has an input color conversionprocessing section 403, a multi color shading (MCS) processing section404, an ink color conversion processing section 405, and a head shading(HS) processing section 406. The image processing unit 402 further has atone reproduction curve (TRC) processing section 407 and a quantizationprocessing section 408. The ink color conversion processing sectioncomposes a second conversion means.

In the image processing unit 402, first, the input color conversionprocessing section 403 converts image data inputted from the input unit401 to image data corresponding to a color reproduction zone of aprinter. The inputted image data is data showing color coordinates (R,G, B) within a color space coordinate, such as RGB, that are expressioncolors of a monitor in the present embodiment. The input colorconversion processing section 403 converts each of the input eight-bitimage data R, G, B to image data (R′, G′, B′) of the color reproductionzone of the printer by a known method such as matrix operationprocessing and processing using a three-dimensional lookup table. Theimage data (R′, G′, B′) is a color signal composed of three elements. Inthe present embodiment, conversion processing is performed using athree-dimensional lookup table together with interpolation operation.Eight-bit image data dealt with in the image processing unit 402 has aresolution of 600 dpi, and binary data obtained by quantization in thequantization processing section 408 has a resolution of 1200 dpi, aswill be described.

The multi color shading (MCS) processing section 404 performs correctionprocessing on image data (a first color signal) converted by the inputcolor conversion processing section 403, thereby converting the imagedata to a second color signal. This processing is also performed using athree-dimensional lookup table (correction table), as will be describedlater. The three-dimensional lookup table is composed of a color cube ofa color signal composed of three elements. This correction processingcan reduce the color shift even if there are ejection volume variationsamong the nozzles of the print head of an output unit 409. A specifictable content on this MCS processing section 404 and correctionprocessing using this table will be described later.

The ink color conversion processing section 405 converts each of R, G, Beight-bit image data processed by the MCS processing section 404 toimage data that is ink color signal data to be used in the printer.Since the printer 100 of the present embodiment uses black (K), cyan(C), magenta (M) and yellow (Y) inks, image data of the RGB signal isconverted to image data composed of eight-bit color signals K, C, M, Y.This color conversion is also performed using a three-dimensional lookuptable together with interpolation operation, as with the aforementionedinput color conversion processing section. As another conversion method,matrix operation processing may be used, as with the above.

The head shading (HS) processing section 406 inputs image data of an inkcolor signal, and converts the imputed eight-bit image data to imagedata of an ink color signal corresponding to an injection volume of eachof the nozzles of the print head by each ink color. That is, thisprocessing is the same as the aforementioned conventional head shadingprocessing. In the present embodiment, this HS processing is performedusing a first-dimensional lookup table. When the present invention isapplied, this HS processing section may not be provided if not otherwisespecified. That is, there are cases where the accuracy of correctionprocessing by the MCS processing section is sufficient relative tomemory capacity, depending on the specification of a printer. In suchcases, processing by the HS processing section can be covered by thecorrection processing in the MCS processing section.

The tone reproduction curve (TRC) processing section 407 performscorrection on the image data composed of the eight-bit ink color signalsthat were subjected to HS processing thereby to adjust the number ofdots to be printed by the output unit 409 for each ink color. That is,there are cases where a relationship between the number of dots to beprinted on a print medium and a brightness realized by the number ofdots is not linear. The TRC processing section 407 corrects theeight-bit image data so as to make this relationship linear, adjustingthe number of dots to be printed on the print medium.

The quantization processing section 408 performs quantization processingon the image data composed of the respective eight-bit (256 values) inkcolors processed in the TRC processing section 407 to obtain one-bitbinary data. In doing so, according to the present embodiment, theeight-bit data is first converted to three-bit, 5-valued index data of“0” to “4” for each color. This index data “0” to “4” corresponds to apattern in which zero to four dots are arranged in 2×2 pixels at aresolution of 1200 dpi. It should be appreciated that a mode ofquantization 408 is not limited to this mode in applying the presentinvention. For example, eight-bit image data may be directly binarizedto obtain binary data (dot data). As a method for quantizationprocessing, the present embodiment uses an error diffusion method, butother pseudo halftone processing such as a dither method may be used.

The output unit 409 drives the print head to eject each color ink toperform printing on the print medium on the basis of the dot data(signals that can be printed) obtained by quantization. The output unit409 specifically is composed of a printing mechanism having the printingheads 101 to 104 illustrated in FIG. 1.

Next, FIGS. 22A to 22C are used to describe a position displacementcorrection of a printing head in the nozzle array direction, which ismade before the MCS processing. As will be described later, the MCSprocessing is processing that, for each unit area on the printingmedium, uses a conversion table to convert image data corresponding to anozzle that performs printing in each unit area. This enables a colordifference between unit areas due to an ejection amount variationbetween nozzles to be reduced. In order to perform the MCS processing,the conversion table should be created for each type of datacorresponding to a nozzle group corresponding to a unit area; however,at the time of the creation, which nozzle corresponds to each unit areashould be already set. That is, before the MCS processing is performed,a correspondence between each unit area on the printing medium and anozzle should be assigned.

The correspondence between each unit area and a nozzle is, inconsideration of an influence of an error at the time of attaching aprinting head, or attaching an ejecting board to the printing head,determined with the printing head being attached to the printer. This isbecause if the printing head is displaced in the nozzle array direction,a nozzle that performs printing in each unit area is changed. In such acase, a so-called “position displacement correction” that corrects adisplacement between a position on the printing medium and a nozzle usedfor printing is made. When the position displacement correction is made,it should be made before the creation of a conversion table thatconverts image data corresponding to a nozzle that performs printing ineach unit area.

FIGS. 22A to 22C are used to describe a position displacement correctionmethod. FIG. 22A illustrates a state where when a plurality of printingheads that eject different inks are attached, position displacement inthe nozzle array direction occurs. In the diagram, the “positiondisplacement correction” is not made. In the diagram, a printing head121 that ejects a cyan ink, and a printing head 122 that ejects amagenta ink are displaced each other in the nozzle array direction(left-right direction in the diagram) by an amount corresponding to twonozzles. In this case, if the inks are ejected from end nozzles of therespective printing heads to thereby attempt to form a blue color dot,because the position displacement occurs between the printing heads, acyan dot 1231 ejected from a cyan nozzle 1211 that is the end nozzle,and a magenta dot 1232 ejected from a magenta nozzle 1221 are notoverlapped, and therefore the blue color dot cannot be formed.

FIG. 22B is a schematic diagram for describing a method for making theposition displacement by adjusting positions of the printing heads inthe printer in the nozzle array direction. By physically aligning theprinting head 121 and the printing head 122 with each other, theadjustment is made so as to align the cyan nozzle 1211 and the magentanozzle 1221 with each other with respect to the conveying direction ofthe printing medium to thereby overlap the dots. Based on this method,the cyan dot ejected from the cyan nozzle 1211 and the magenta dotejected from the magenta nozzle 1221 are land on the same position, andthereby a blue dot 1233 can be formed. This method is one that uses ascrew or the like for an alignment reference to mechanically adjustattachment positions of the printing heads with respect to the printer.

FIG. 22C is a schematic diagram for describing a method for making theposition displacement by correcting image data distributed to eachnozzle of the printing heads. In this method, when the image data areallocated to the respective printing heads, nozzles to which the imagedata for forming the respective color dots to be arrayed to the sameposition in the nozzle arrangement direction are allocated are changedto the nozzles which are arrayed in the same position in the nozzlearrangement direction. In the case of the diagram, a change is made suchthat image data allocated to the magenta nozzle 1221 of the printinghead 122 in FIG. 22A are allocated to a magenta nozzle 1223. Based onthis method, the cyan dot ejected from the cyan nozzle 1211 and amagenta dot ejected from the magenta nozzle 1223 land on the sameposition, and thereby a blue dot 1234 is formed. Similarly, for theother nozzles, image data to be allocated are displaced in the nozzlearray direction by the amount corresponding to two nozzles, and therebycorrections can be made.

As described above, in the case of position displacement betweenprinting heads, the method that adjusts positions of the printing headsin the nozzle array direction to thereby align nozzles, and the methodthat a nozzle to which image data are allocated is changed to a nozzlealigned in the conveyance direction are known. Based on any of thesemethods, a placement position displacement occurring when a plurality ofprinting heads for different ink colors are displaced each other in thenozzle arrangement direction can be corrected.

By making such a position displacement correction, a correspondencerelationship between nozzles corresponding to each unit area is set. Asdescribed above, the MCS processing that is a feature of the presentinvention should be performed with the correspondence between each unitarea on the printing medium and a nozzle being set. If a position in theconveying direction is not displaced, it is not necessary to make theposition displacement correction; however, in the case of making theposition displacement correction, the position displacement correctionshould be made at timing before the MCS processing to make alignment.Note that the position displacement correction method is not limited toany of the above two methods, but may be any other method if the methodincludes a process for setting the correspondence relationship between aunit area and a nozzle.

FIGS. 5A and 5B are flow charts illustrating data processing forgenerating parameters of a table to be used by an MCS processing section404 illustrated in FIG. 4A and processing by the MCS processing section404 using the table in image processing for generating print data,respectively.

In FIG. 5A, processing S510 generates parameters of a three-dimensionallookup table to be used by the MCS processing section 404 and hasprocesses in Steps S502 to S506. In the present embodiment, theprocessing S510 is performed when a printer is manufactured, has beenused for a predetermined period, or has performed a predetermined amountof printing. That is, the processing S510 also can be performed ascalibration, which updates table parameters that are the content of thelookup table. Processing S520 illustrated in FIG. 5B is performed by theMCS processing section 404 when printing is performed by a printer,which is part of image processing performed by the image processing unit402 illustrated in FIG. 4A in order to generate print data. Thisprocessing has processes in Steps S507 and S508. It should beappreciated that a timing for performing generation processing of tableparameters is not limited to the aforementioned timing in applying thepresent invention. For example, the generation processing may beperformed before the processing S520 for printing is performed.

First, processing S510 to generate table parameters illustrated in FIG.5A will be described.

In the present embodiment, after table parameters for the HS processingsection 406 are generated, table parameters for the MCS processingsection are generated. Therefore, at the time point of Step S501 onwhich this processing is started, table parameters for the HS processingunit have been already generated (updated). In this generation of tableparameters in the HS processing section, it is assumed that there areejection volume variations among the nozzles of the magenta ink printhead 103 illustrated in FIG. 3A. Table parameters corresponding to theprint head 103 are parameters illustrated in FIG. 3B, which, in otherword, the parameters for performing correction so that the number of dotdata in a region corresponding to four nozzles 10321 on the right halfis half the number of dot data in a region corresponding to four nozzles10311 on the left half, as illustrated in FIG. 3B. If each nozzle of thecyan ink print head 102 has an ejection property illustrated in FIG. 3A,that is, if all the nozzles have a normal ejection volume, tableparameters for the HS processing section are parameters so as to convertimage data as what it is. In this way, according to the presentembodiment, when table parameters for the MCS processing section aregenerated or updated, the table parameters for the HS processing sectionare generated prior to this. This can properly reduce a color shift dueto the variations among nozzles by total processing of the MCSprocessing section and HS processing unit.

First, in Step S502, for each set of R, G, B representing a color whosecolor shift tends to be large of image data represented by a set of R,G, B to be inputted to the MCS processing section, ink is ejected fromall the nozzles of the print head illustrated in FIG. 1, therebyprinting an image for measurement (patch) on a print medium.Specifically, 0 to 255 of each of R, G, B are divided by, e.g. 17 toobtain values; grid points whose color shift tendency is significantlychanging are selected from grid points set by combinations of theobtained values; and an image for measurement is printed for sets of R,G, B corresponding to these grid points. This grid point of a colorwhose color shift tendency is large can be selected from the grid pointsset by combinations of the values obtained by dividing by 17 bypreviously knowing a color whose color shift is significant, such as aset of R=0, G=0, B=255 corresponding to a blue image described withreference to FIGS. 3A to 3C. It should be appreciated that selectinggrid points of a color for printing an image for measurement is notlimited to the above example. For example, sets of R, G, B whose colorshift is larger than a predetermined color shift may be set, and imagesfor measurement may be printed for all of these sets. In other words,sets of color signals for printing an image for measurement can be setdepending on an operation load and a memory capacity.

According to the present embodiment, in each of data of an image formeasurement set as described above, a resolution of a plurality ofpixels composing the data is 600 dpi. In the data of the plurality ofpixels, when sets of R, G, B values of data of the image for measurementare the same, the color is uniform. Image data of the image formeasurement is eight-bit image data (hereinafter referred to as devicecolor image data D[X]) that was subjected to processing by the inputcolor conversion processing section 403 illustrated in FIG. 4A. Theimage data is inputted through a bypass processing path indicated by adash line 410 in FIG. 4A to the ink color conversion processing section405, without being subjected to processing by the MCS processing section404. Specifically, the MCS processing section 404 performs correctionprocessing on the device color image data D [X], using a table in whicha correction amount indicated by a table parameter is zero. After that,the image data proceeds to the HS processing section 406, TRC processingsection 407 and quantization processing section 408, and then is printedon the print paper 106 in the output unit 409. In this process, imagedata of the image for measurement is converted to image data of inkcolor signals by the ink color conversion processing section 405, anddata having 100% cyan duty and 100% magenta duty that forms bluedescribed above with reference to FIGS. 3A to 3C, can be obtained as oneof the data of the image for measurement. That is, data of (K, C, M,Y)=(0, 255, 255, 0) is obtained as image data of the image formeasurement. Then, the obtained data is subjected to processing by theHS processing section 406 and its subsequent processing, resulting inthe image data for measurement composed of dot data illustrated in FIG.3B. In the following description, generation processing will bedescribed on only table parameters corresponding to grid pointsindicative of image data of this blue image for measurement, to simplifydescription.

In device color image data D[X], X is a value to specify pixels with aresolution of 600 dpi in image data for measurement. In other words, Xis a value for specifying, as a unit of 300 dpi, a pixel region(hereinafter referred to as area) corresponding to contiguous fournozzles in a nozzle arrangement of each ink color print head illustratedin FIG. 1. Accordingly, since a resolution of dots printed correspondsto the resolution of the nozzle arrangement and is 1200 dpi, two pixelsof the image data D [X] having a 600 dpi resolution corresponds to oneof the aforementioned area and is specified as X. As described above,this device color image data D[X] is subjected to processing by the inkcolor conversion processing section 405 and it subsequent processing,and the image for measurement of the data is printed in the output unit409.

FIGS. 6A and 6B are diagrams illustrating printing of an image formeasurement in Step S502. In FIGS. 6A and 6B, elements identical tothose illustrated in FIGS. 3A to 3C have the same reference charactersand will not be described.

FIG. 6A, as with the example illustrated in FIG. 3A, illustrates anexample in which four nozzles on the right in FIG. 6A of nozzles of themagenta print head 103 have a larger ejection volume than a normalejection volume. In this case, a blue image for measurement illustratedin FIG. 6B is printed. That is, an image for measurement is printed inwhich a region on the right in FIG. 6B has a color shift and the blue ofthe region is different from the blue on the left region in FIG. 6B.

Returning to FIG. 5A, in the next Step S503, as described above, thecolor of an image for measurement printed on the print paper 106 ismeasured to obtain color information B[X]. According to the presentembodiment, the printer illustrated in FIG. 1 includes a scanner 107that measures the image for measurement. Accordingly, this processing inStep S503 includes receiving the data measured by the scanner.Alternatively, a scanner separate from a printer may be used to performmeasurement by operation of a user. The scanner and printer may beconnected by signals and the measurement results may be automaticallyinputted from the scanner to the printer, for example. In the presentembodiment, color information B[X] is represented by sets of RGB valuesread by the scanner. However, any data format, such as L*a*b* measuredby a colorimetric device, can be used.

In the present embodiment, the resolution of the aforementionedmeasurement is 600 dpi. Meanwhile, the resolution of printed dots is1200 dpi that corresponds to the resolution of the nozzles. Accordingly,in the aforementioned color measurement, a region corresponding to fournozzles illustrated in FIG. 6B is measured as two pixels. Then, thecolor information B[X] is obtained as a unit of a region correspondingto the two pixels of the measurement (the aforementioned area). That is,in the color information B[X], X is a value to specify an area, and isobtained as an average value of the measurement results of the twopixels of the measurement. In the example illustrated in FIG. 6B, insuch a way that an area corresponding to four nozzles on the left sideand an area corresponding to four nozzles on the right side are deemedto be different areas, the color information B[X] is obtained for eachof the areas.

In this way, a blue image for measurement of a grid point whose devicecolor image data D[X] is (R, G, B)=(0, 0, 255) is printed by ejectinginks from all of the nozzles of the cyan and magenta print heads 102 and103 illustrated in FIG. 1. Then, color information B[X] is obtained foran area unit corresponding to the four nozzles. FIG. 6B illustrates aportion of the area; hereinafter an area on the left in FIG. 6B will bereferred to as a first area (X=1) and an area on the right in FIG. 6Bwill be referred to as a second area (X=2). Color information of thefirst area is set to B[1]=(R1, G1, B1) and color information of thesecond area is B[2]=(R2, G2, B2). An example illustrated on the rightarea in FIG. 6B illustrates a case where all four magenta nozzles have alarger ejection volume than a normal ejection volume. Naturally, therecan be also a case where three of four nozzles may have a largerejection volume than a normal ejection volume and remaining one has anormal ejection volume, for example. In this case, needless to say, theobtained value B[2] that is the color information of the second area isdifferent from the aforementioned case.

Next, in Step S504 of FIG. 5A, a color shift amount T[X] of each area[X] is calculated from a target color A=(Rt, Gt, Bt) and the colorinformation B[X] obtained in Step S503. Here, the target color A iscolor data obtained by measuring with a scanner an image printed by therespective color printing heads having a normal ejection volume in theoutput unit 409 on the basis of the same blue image data represented by(R, G, B)=(0, 0, 255). In the present embodiment, the resolution of themeasured color data is 300 dpi, as described above. Therefore, also inprocessing to generate table parameters by the MCS processing section inthe aforementioned Step S504 and the undermentioned Steps S505 and S506,data with a pixel resolution of 300 dpi is processed.

That is, a color shift amount T is represented as follows:

Color shift amount T[1]=B[1]−A=(R1−Rt,G1−Gt,B1−Bt)

Color shift amount T[2]=B[2]−A=(R2−Rt,G2−Gt,B2−Bt)

Here, the color shift amount T [1] is a difference between a blue colorby overlapping a cyan ink having a normal ejection volume and a magentaink having a normal ejection volume in an area on the left in theexample of FIG. 6B and a blue color of the target color data A. Exceptfor a measurement error, the color shift amount T[1] is ideally zero,that is, fulfills the relationship of R1=Rt, G1=Gt, B1=Bt.

Meanwhile, the color shift amount T[2] is a difference between a bluecolor by combination of a cyan ink having a normal ejection volume and amagenta ink having a larger ejection volume than a normal ejectionvolume on the right in the example of FIG. 6B and a blue color of thetarget color data A. For example, if the blue color observed bycombination of a cyan area 10623 and a magenta area 10625 cyan has astronger blue cast in comparison with the target blue color, the colorshift amount T[2] is a color shift amount whose cyan color is large.That is represented by R2<Rt, G2=Gt, B2=Bt, for example.

Returning to FIG. 5A, in the next Step S505, a correction value T⁻¹[X]is calculated from the color shift amount T[X] of each area [X]. In thepresent embodiment, an inverse transformation equation is simply used asfollows:

T ⁻¹ [X]=−T[X]

Accordingly, a correction value of each area is:

Correction value T ⁻¹[1]=−T[1]=A−B[1]=(Rt−R1,Gt−G1,Bt−B1)

Correction value T ⁻¹[2]=−T[2]=A−B[2]=(Rt−R2,Gt−G2,Bt−B2)

Here, the correction value T⁻¹[1] corresponds to an area on the left inFIG. 6B and is ideally zero. Meanwhile, the correction value T⁻¹[2]corresponds to an area on the right in FIG. 6B and reduces cyan color inthe aforementioned example. That is, in the case of R2<Rt, Rt−R2 is apositive value, which increases redness and reduces cyan color.

Next, in Step S506 of FIG. 5A, an equivalent correction value Z⁻¹[X] iscalculated from a correction value T⁻¹[X] of each area [X]. That is,since a correction value T⁻¹[X] is a correction value of blue color in ameasurement color space, an equivalent correction value Z⁻¹[X] iscalculated on the basis of this correction value so that equivalentcorrection value Z⁻¹[X] corrects a blue color in a device color space bythe same amount of this correction value T⁻¹[X]. Here, the equivalentcorrection value Z⁻¹[1] corresponds to an area on the left in FIG. 6Band is ideally zero. Meanwhile, an equivalent correction value Z⁻¹[2]corresponds to an area on the right in FIG. 6B and reduces a cyan color.

If a measurement color space is identical to a device color space, therelationship is as follows:

Z ⁻¹[1]=T ⁻¹[1]=−T[1]=A−B[1]=(Rt−R1,Gt−G1,Bt−B1)

Z ⁻¹[2]=T ⁻¹[2]=−T[2]=A−B[2]=(Rt−R2,Gt−G2,Bt−B2)

However, they are not identical to each other in most cases. In thesecases, color space conversion is performed. That is, if linearconversion can be performed between the both color spaces, a knownmethod such as the following matrix conversion can be used.

$\begin{matrix}{{{Z^{- 1}\lbrack 1\rbrack} = {\begin{bmatrix}{a\; 1} & {a\; 2} & {a\; 3} \\{a\; 4} & {a\; 5} & {a\; 6} \\{a\; 7} & {a\; 8} & {a\; 9}\end{bmatrix} \times \begin{bmatrix}{{Rt} - {R\; 1}} \\{{Gt} - {G\; 1}} \\{{Bt} - {B\; 1}}\end{bmatrix}}}{{Z^{- 1}\lbrack 2\rbrack} = {\begin{bmatrix}{a\; 1} & {a\; 2} & {a\; 3} \\{a\; 4} & {a\; 5} & {a\; 6} \\{a\; 7} & {a\; 8} & {a\; 9}\end{bmatrix} \times \begin{bmatrix}{{Rt} - {R\; 2}} \\{{Gt} - {G\; 2}} \\{{Bt} - {B\; 2}}\end{bmatrix}}}} & \lbrack{Expression}\rbrack\end{matrix}$

Here, a1 to a9 are conversion coefficients for converting a measurementcolor space to a device color space. If linear conversion cannot beperformed between the both color spaces, a known method such as athree-dimensional lookup table can be used to obtain the value asfollows:

Z ⁻¹[1]=F(Rt−R1,Gt−G1,Bt−B1)

Z ⁻¹[2]=F(Rt−R2,Gt−G2,Bt−B2)

where F is a function for converting a measurement color space to adevice color space. Conversion relationship of the lookup table is inconformity to the function F.

If the relationship between a correction value T⁻¹ [X] and an equivalentcorrection value Z⁻¹[X] varies depending on a color, a known method suchas a three-dimensional lookup table can be similarly used to obtain thevalue as follows:

Z ⁻¹[1]=F(Rt,Gt,Bt)−F(R1,G1,B1)

Z ⁻¹[2]=F(Rt,Gt,Bt)−F(R2,G2,B2)

where F is also a function for converting a measurement color space to adevice color space.

In this way, for a grid point selected as a color whose color shifttendency is significantly changing, a table parameter that is grid pointdata can be obtained for an area [X] corresponding to a nozzle. Tableparameters of grid points other than the selected grid points can beobtained by interpolation between the selected grid points. As a methodusing interpolation, a well-known method can be used and will not bedescribed.

An equivalent correction value Z⁻¹[X] obtained as described above, whichis a table parameter of each grid point, is associated with the gridpoint for each area [X] and stored in the HDD 303 (FIG. 2) of the hostPC.

Next, processing S520 performed by the MCS processing section 404illustrated in FIG. 5B will be described. That is, in a series of imageprocessing by the respective processing sections illustrated in FIG. 4A,the MCS processing section 404 corrects image data using thethree-dimensional lookup table for each area that has a correction valueobtained as described above as grid point data.

First, in Step S507, an equivalent correction value Z⁻¹[X] generated asabove, which is a table parameter of the MCS processing section, isapplied to device color image data D[X] thereby to perform correction.

In this step, first, it is determined which area of the aforementionedarea [X] includes a pixel of interest to be subjected to imageprocessing. Here, a pixel of image processing has a resolution of 600dpi whereas an area [X] is specified by a resolution of 300 dpi.Accordingly, two pixels correspond to or belong to one area [X].

When X=n, a value of the area [X] that includes the pixel of interest isobtained, a set of R, G, B illustrated by image data of the pixel ofinterest and a table stored in the HDD 303 is referred to for the area[n] thereby to obtain an equivalent correction value Z⁻¹[n]corresponding to the set of R, G, B and area. For example, if a set ofR, G, B indicated by image data of a pixel of interest is (0, 0, 255)and represents a blue image, an equivalent correction value Z⁻¹[n] ofblue can be obtained as described above. Then, correction is performedby applying the equivalent correction value Z⁻¹[n] to the image data ofthe pixel of interest.

Specifically, the MCS processing section 404 applies an equivalentcorrection value Z⁻¹[X] to device color image data D[X] corresponding toan area [X] that a pixel of interest belongs to according to thefollowing expression, thereby generating corrected device color imagedata D′[X]:

device color image data D′[1]=D[1]+Z ⁻¹[1]

device color image data D′[2]=D[2]+Z ⁻¹[2]

where Z⁻¹[1] is a correction value corresponding to an area [1] on theleft in the blue example of FIG. 6B and is ideally zero, as describedabove. Accordingly, the corrected device color image data D′[1]represents the same blue as the target color A. Meanwhile, Z⁻¹[2] is acorrection value corresponding to an area [2] on the right in the blueexample of FIG. 6B and reduces cyan color, as described above.Accordingly, the corrected device color image data D′[2] represents bluewhose cyan color has been reduced by correction relative to the targetcolor A.

Next, in Step S508, the device color image data corrected as aboveproceeds through the ink color conversion processing section 405, HSprocessing section 406, TRC processing section 407 and quantizationprocessing section 408 to the output unit 409, where the image data isprinted on the print paper 106.

FIGS. 7A and 7B are diagrams illustrating an image printed in Step S508of FIG. 5B. FIG. 7A, as with FIG. 6A, illustrates ejection volumeproperties of nozzles of the cyan print head 102 and magenta print head103. When correction is performed on the image illustrated in FIG. 7A bythe MCS processing, dots without overlapping of cyan dots, such asmagenta dots 10626 in an area on the right in FIG. 7B exist. That is,cyan dots were still printed on the magenta dots 10626 after HSprocessing in FIG. 6B. After MCS processing, a cyan color of image dataD′[2] is reduced relative to the target color A, resulting in decreaseof the number of the cyan dots.

Here, in each printing area illustrated in FIG. 7B, a color shift amountT[X] occurs due to ejection volume variations and so on in printing.That causes the following relationships:

color information of an area on the left≈color on print papercorresponding to D′[1]+T[1]≈A

color information of an area on the right≈color on print papercorresponding to D′[2]+T[2]≈A

where, D′[1] is ideally the same blue color as the target color A andT[1] is ideally zero. D′[2] is a blue color whose cyan color has beenreduced by T[2] relative to the target color A, where T[2] is a colorshift amount to increase a cyan color. In this way, the blue color of anarea on the left and the blue color on an area on the right becomealmost the same, thereby reducing an uneven color due to a color shift.

As described above, in the present embodiment, for color (a set of R, G,B) whose color shift tendency is significantly changing, an image formeasurement (patch) is printed on a print medium, and a table parameteris obtained on the basis of the measurement result. That is because acolor shift amount that causes a color shift depends on both of (1) acolor printed on a print region and (2) a combination of printingproperties of respective colors to be printed on the print region, dueto the principle of color shift occurrence. Here, (2) the printingproperties of respective ink colors include factors that affect a dotdiameter, such as a dot shape, an ink penetration rate and a printmedium type, in addition to the ejection volume described above. It isobvious that a color shift amount depends on a combination of printingproperties of ink colors used to print the color and does not depend onprinting properties of inks that are not used. Accordingly, the type andnumber of ink colors varies depending on the color of a pixel ofinterest. Therefore, in some colors, only one ink color is involved anda color shift amount may not exist.

Here, by way of example, the case where a measurement color space isidentical to a device color space will be described. For example, sincea cyan mono-color (R=0, G=255, B=255) has already a uniform densityafter HS processing and does not have a color shift, it is preferablenot to perform correction in the MCS processing section 404. Therefore,the equivalent correction value is preferably Z⁻¹[1]=Z⁻¹[2]=0=(0, 0, 0).Since magenta mono-color (R=255, G=0, B=255) also has a uniform densityafter HS processing and does not have a color shift, it is preferablenot to perform correction in the MCS processing section 404. Therefore,the equivalent correction value is Z⁻¹[1]=Z⁻¹[2]=0=(0, 0, 0). Meanwhile,a blue color (R=0, G=0, B=255) has a high possibility of a color shifteven if it is subjected to HS processing, as described with reference toFIGS. 3A to 3C. Therefore, in the example illustrated in FIG. 6B, anequivalent correction values are as follows:

equivalent correction value Z ⁻¹[1]=0=(0,0,0)

equivalent correction value Z ⁻¹[2]=T ⁻¹[2]=(Rt−R2,Gt−G2,Bt−B2)

That is, even if the color signal value B is B=255, a color shift amountvaries depending on a combination of other colors R, G and therefore asuitable equivalent correction value also varies.

In other words, in generating the table as described above, a grid pointof a color whose color shift tendency is significantly changing isselected so that each grid point in the table has the aforementionedsuitable equivalent correction value as grid point data. Then, the MCSprocessing section 404 uses a three-dimensional lookup table obtained onthe basis of the measurement result of an image for measurement of acolor of the grid point suitably selected as described above.

Another example of processing S510 to generate table parameters for theMCS processing section can be as follows.

First, a plurality of patches (images for measurement) in which valuesof device colors R, G, B are independently changed are printed by theprint heads illustrated in FIG. 1. FIG. 8 illustrates distribution ofcolors of grid points in a device color space, in which each color hasthree gradations (0, 128, 255) and total 3×3×3=27 grid points areprinted on the basis of combinations of the three gradations. FIG. 8illustrates an RGB color space in which 801, 802 and 803 indicate redaxis, green axis and blue axis, respectively. Grid points indicated byblack circles represent colors for patch printing. Grid points indicatedby 804 to 806 are the colors described as examples in the aforementionedembodiment; and 804, 805 and 806 indicate cyan, magenta and blue colors,respectively. A table structure indicated by these grid points in FIG. 8is the same as that described with reference to FIGS. 5A and 5B, exceptfor how to generate correction data other than the 27 grid points asfollows.

First, a patch is printed on the basis of device color (Rn, Gn, Bn) foreach of the 27 grid points, and each patch is subjected to colorimetryto obtain a measurement value (Rp, Gp, Bp) for each patch. Next, a patchis printed on the basis of device color (Ri, Gi, Bi) for each of pointsother than the 27 grid points, and this patch is measured to obtainmeasurement value (Rt, Gt, Bt). Next, the patch color (Rp, Gp, Bp) thatis the most similar to the measurement value (Rt, Gt, Bt) is selected toobtain device color (Rn, Gn, Bn) corresponding to the selected patchcolor. How to select the most similar patch color is as follows:

√{square root over ((Rt−Rp)²+(Gt−Gp)²+(Bt−Bp)²)}{square root over((Rt−Rp)²+(Gt−Gp)²+(Bt−Bp)²)}{square root over((Rt−Rp)²+(Gt−Gp)²+(Bt−Bp)²)}

A patch to print (Rp, Gp, Bp) is selected such that the solution of theabove expression is minimum. Then, for the device color (Ri, Gi, Bi), acorrection table is generated on the basis of a correction table of thedevice color (Rn, Gn, Bn) and is used in the MCS processing section.Practically, accuracy of correction other than the 27 grid points can beimproved by printing in more gradations than those illustrated in FIG.8, or by using a known method, such as interpolating a plurality ofpatches during estimation. A known interpolation method includestetrahedral interpolation and cubic interpolation. In the case oftetrahedral interpolation, calculation may be performed by interpolatingfrom four surrounding grid points that form a tetrahedral containing ameasurement value (Rt, Gt, Bt). In the case of cubic interpolation,calculation may be performed by interpolating from eight surroundinggrid points that form a cube containing a measurement value (Rt, Gt,Bt).

An example of a patch color suitable for MCS processing will bedescribed below. When each of RGB in FIG. 8 is evenly divided to Ngradations and a patch is printed, N̂3 patches are printed. For example,if N=9, 729 patches are printed, and if N=17, 4913 patches are printed.If a length of one patch is, for example, 5 mm, a print paper of about3.5 m is required to print 729 patches and a print paper of about 25 mis required to print 4913 patches.

FIG. 12 is a diagram illustrating a patch color suitable for MCSprocessing.

Since 1201 to 1206 in FIG. 12 correspond to 801 to 806 in FIG. 8, theywill not be described.

A portion indicated by a thick dash line 1207 shows a patch colorsuitable for MCS processing.

The thick dash line 1207 is composed of the following 12 line segments:

TABLE 1 Black (R = 0, G = 0, B = 0) to Red (R = 255, G = 0, B = 0) Black(R = 0, G = 0, B = 0) to Green (R = 0, G = 255, B = 0) Black (R = 0, G =0, B = 0) to Blue (R = 0, G = 0, B = 255) Red (R = 255, G = 0, B = 0) toMagenta (R = 255, G = 0, B = 255) Red (R = 255, G = 0, B = 0) to Yellow(R = 255, G = 255, B = 0) Green (R = 0, G = 255, B = 0) to Cyan (R = 0,G = 255, B = 255) Green (R = 0, G = 255, B = 0) to Yellow (R = 255, G =255, B = 0) Blue (R = 0, G = 0, B = 255) to Cyan (R = 0, G = 255, B =255) Blue (R = 0, G = 0, B = 255) to Magenta (R = 255, G = 0, B = 255)Cyan (R = 0, G = 255, to White (R = 255, B = 255) G = 255, B = 255)Magenta (R = 255, G = 0, to White (R = 255, B = 255) G = 255, B = 255)Yellow (R = 255, G = 255, to White (R = 255, B = 0) G = 255, B = 255)

If the thick dash line 1207 in FIG. 12 is divided to N gradations and apatch is printed, (N−2)×12+8 patches are printed. For example, in thecase of N=5, 44 patches are printed; in the case of N=9, 92 patches areprinted; and in the case of N=17, 188 patches are printed, which is lessthan 216 patches in the case of N=6 in FIG. 8.

In the present embodiment, only patches on this thick dash line 1207,which are grid points of respective edges of a color cube, are printedand subjected to colorimetry, and from the result of the colorimetry, acolor inside the thick dash line 1207 is estimated. This permits finelyobtaining a colorimetry value at the outermost of a color regionreproduced by a printer.

With reference to FIGS. 13 and 14, a method to estimate a color otherthan patches on the thick dash line 1207 of the color cube in FIG. 12will be described. In the present embodiment, an example in the case ofN=5 will be described to simplify the description.

First, colors of six surfaces in the color cube are estimated. Sixsurfaces are surfaces, each fulfilling a condition that RGB is R=0(minimum value), R=255 (maximum value), G=0 (minimum value), G=255(maximum value), B=0 (minimum value), or B=255 (maximum value).

FIG. 13 is a diagram illustrating an example in which a color Z ofcoordinates (Rin, 0, Bin) in the surface of G=0 is estimated. In FIG.13, 1301 to 1306 correspond to 1201 to 1206 in FIG. 12 and thereforewill not be described. In FIG. 13, white circle portions indicate printpatches in the case of N=5, and colorimetry values already exist forthese white circle portions.

A thick dash line 1307 indicates a portion surrounding the surface ofG=0 of the printed patches. The surface of G=0 are surrounded by fouredges: black (0, 0, 0) to blue (0, 0, 255), blue (0, 0, 255) to magenta(255, 0, 255), red (255, 0, 0) to magenta (255, 0, 255), and black (0,0, 0) to red (255, 0, 0) edges. Here, an estimate value of a color Z foran input value of the color (Rin, 0, Bin) in the surface of G=0 can becalculated in two calculation methods. In a first calculation method,the estimate value of color Z is calculated from a color X correspondingto (0, 0, Bin) of black to blue colorimetry values and a color Ycorresponding to (255, 0, Bin) of red to magenta colorimetry valuesaccording to the following expression:

Z estimate value 1=(Y*Rin)+(X*(255−Rin))/255

In a second calculation method, the estimate value of color Z iscalculated from a color I corresponding to (Rin, 0, 0) of black to redcolorimetry values and a color J corresponding to (Rin, 0, 255) of blueto magenta colorimetry values according to the following expression:

Z estimate value 2=(J*Bin)+(I*(255−Bin))/255

In the present embodiment, a final Z estimate value is an average valueof the aforementioned Z estimate value 1 and Z estimate value 2.

This method is termination of estimating a color (Rin, 0, Bin) in thesurface of G=0. Similarly, the remaining colors in the surface of G=0are estimated. In the case of N=5, colors of total (N−2)̂2=9 points areestimated.

Similarly, colors in the remaining five surfaces are estimated. In thisway, in the case of N=5, colors of total (N−2)̂2*6=54 points in the totalsix surfaces are estimated.

Next, a color inside the color cube is estimated (interpolated).

FIG. 14 is a diagram illustrating an example in which a color ofcoordinates (Rin, Gin, Bin) inside the color cube. 1401 to 1406 in FIG.14 correspond to 1301 to 1306 in FIG. 13 and therefore will not bedescribed.

White circle portions in FIG. 14 indicate colors that are printedpatches and have been estimated in the case of N=5, and thereforecolorimetry values or estimate values already exist for these whitecircle portions. That is, they include a grid point whose three elementsare equal and a grid point whose two of three elements are equal and theremaining one element is a minimum or maximum value.

A thick dash line 1407 surrounds a portion of the surface of G=Gin ofthe printed patches and estimate values. The surface of G=Gin issurrounded by four edges: (0, Gin, 0) to (0, Gin, 255), (0, Gin, 255) to(255, Gin, 255), (255, Gin, 0) to (255, Gin, 255), and (0, Gin, 0) to(255, Gin, 9) edges.

Here, an estimate value of a color Z for an input value of a color (Rin,Gin, Bin) in the surface of G=Gin can be calculated in two methods. In afirst method, an estimate value of color Z is calculated from a color Xcorresponding to (0, Gin, Bin) and a color Y corresponding to (255, Gin,Bin) according to the following expression:

Z estimate value 1=(Y*Rin)+(X*(255−Rin))/255

In a second method, an estimate value of color Z is calculated from acolor I corresponding to (Rin, Gin, 0) and a color J corresponding to(Rin, Gin, 255) according to the following expression:

Z estimate value 2=(J*Bin)+(I*(255−Bin))/255

In a method to estimate a color of coordinates (Rin, Gin, Bin) inside acolor cube, two estimate values can be similarly calculated from each ofa surface of R=Rin and a surface of B=Bin, in addition to theaforementioned method to estimate from the surface of G=Gin.

Therefore, in the present embodiment, a final Z estimate value is anaverage value of six estimate values that are the Z estimate value 1 andZ estimate value 2 calculated from the three surfaces of R=Rin, G=Gin,and B=Bin, respectively.

This method is termination of estimating a color of coordinates (Rin,Gin, Bin) inside the color cube. Similarly, the remaining colors ofcoordinates inside the color cube are estimated. In the case of N=5,colors of total (N−2)̂3=27 points are estimated in the whole of inside ofthe color cube.

By estimating described above, 81 estimate values are calculated fromthe colorimetry values of 44 print patches in the case of N=5, therebyobtaining color information of total 5̂3=125 points.

Next, in the MCS processing parameter generation process 510, by usingthis color information, patch colors (+estimate colors) Rp, Gp, Bp,which are the most similar to target colors RT, GT, BT of the devicecolors Ri, Gi, Bi, are estimated. Next, device colors Rn, Gn, Bncorresponding to the patch colors (+estimate colors) are estimated.

Then, a correction table to convert the device colors (Ri, Gi, Bi) tothe device colors (Rn, Gn, Bn) is generated.

This permits accurately generating a correction table with a smallnumber of patches.

The MCS processing section 404 must have a configuration to change acorrection content depending on each print region as a color shiftamount correction method depending on a combination of respective inkcolor ejection volumes.

That is, for example, the MCS processing section may have athree-dimensional lookup table for each print region and may change thethree-dimensional lookup table depending on the print region.

As described above, the present invention performs MCS processing forconverting image data for an image to be printed on the print area byusing the conversion table to reduce the color difference of compositecolor printed between the print areas, when the respective print area isprinted by using inks of two or more colors. The print area is one of aplurality of unit areas into which the printable area is divided withrespect to the nozzle arrangement direction. The MCS processing that isperformed by using the conversion table for every print area can reducethe color difference of the composite color, that the conventional headshading processing that is performed by using one dimensional LUT cannot reduce.

Further, MCS processing of the present embodiment is performed by usingthe conversion table that can simultaneously perform the ink conversionprocess at the ink conversion process unit 404 and the MCS processing.The conversion table is the conversion table that converts the imagedata corresponding to R, G, B into the image data corresponding to C, M,Y, K.

Further, in the present embodiment, it is explained that the print headis provided for every ink color. However, the present invention mayadopt a manner that one print head has nozzle arrays corresponding to aplurality of colors. In the case where the print head is provided forevery ink color as in the present embodiment, it is possible to reducethe color difference which occurs due to the effect of the arrangementerror of the ejection substrate. In the case where a position of thenozzles is shifted due to the arrangement error of the ejectionsubstrate, a color printed by using inks of two or more colors isdifferent from a target color. The present invention can reduce thecolor difference which occurs in the above case because the presentinvention performs the above MCS processing after setting thecorrespondence relationship between the unit area and the nozzles usedfor printing the print area (the unit area). As mentioned above, it ispossible to correct the composite color so as to match thecharacteristics of the nozzles of the print area (the unit area) bysetting the correspondence relationship between the unit area and thenozzles before performing the MCS processing. That is, even if thenozzles for the respective ink colors, which are used for a print of acertain printing area, are formed on the different substrates,respectively, there is a conversion table generated with respect to thenozzles used for the respective ink colors used for the print of theprint area. Accordingly, image data to be printed with nozzlescorresponding to the print area can be corrected and a color differencedue to a position error also can be reduced regardless of an existenceof positional error of the nozzles.

In the present embodiment, print patches are set on 12 line segments asillustrated in FIG. 12, but it is preferable to print patches on the 12line segments plus another seven line segments as illustrated in FIG. 15in order to obtain color information more accurately and moreefficiently.

FIG. 15 is an example of a patch color by which color information can beobtained more accurately and more efficiently. 1501 to 1507 in FIG. 15correspond to 1201 to 1207 in FIG. 12 and therefore will not bedescribed. 1508 are additional seven line segments and each of them isas follows:

TABLE 2 Black (R = 0, G = 0, B = 0) to Cyan (R = 0, G = 255, B = 255)Black (R = 0, G = 0, B = 0) to Magenta (R = 255, G = 0, B = 255) Black(R = 0, G = 0, B = 0) to Yellow (R = 255, G = 255, B = 0) Red (R = 255,G = 0, B = 0) to White (R = 255, G = 255, B = 255) Green (R = 0, G =255, B = 0) to White (R = 255, G = 255, B = 255) Blue (R = 0, G = 0, B =255) to White (R = 255, G = 255, B = 255) Black (R = 0, G = 0, B = 0) toWhite (R = 255, G = 255, B = 255)

If total 19 line segments in FIG. 15 are divided to N gradations andpatches are printed, (N−2)×19+8 patches are printed. For example, in thecase of N=5, 65 patches are printed; in the case of N=9, 141 patches areprinted; and in the case of N=17, 293 patches are printed, which is lessthan 343 patches in the case of N=7 in FIG. 8.

A method for estimating a color inside a color cube in FIG. 15 isperformed as with FIGS. 13 and 14, and colorimetry values of seven linesegments added in FIG. 15 are not subjected to estimation but are usedas they are.

This enables color information such as blue to white to be finelyobtained, and correction tables can be accurately generated using asmall number of patches.

As long as advantageous effects of the present invention can beobtained, a color estimation method is not limited to the interpolationmethod used in description on FIGS. 13 to 15, but another known methodcan be used.

Similarly, FIG. 12 has been described using an example of 12 linesegments, and FIG. 15 has been described using an example of 19 linesegments, but the number of line segments are not limited to 12 and 19.The number of line segments may be 13 to 18 by using some of theadditional seven line segments illustrated in FIG. 15, not all of them.

FIG. 16 illustrates a pattern example obtained by printing print patchesof 12 line segments in FIG. 12 by N=5. In FIG. 16, 106 indicates a printpaper, and 10601 to 10612 each indicates a print patch of each of theline segments. An input RGB value is indicated on the upper edge andlower edge of the each print patch.

FIG. 17 illustrates a pattern example obtained by printing print patchesof seven additional line segments in FIG. 15 by N=5. In FIG. 17, 106indicates a print paper, and 10613 to 10619 each indicates a print patchof each of the additional line segments. An input RGB value is indicatedon the upper edge and lower edge of the each print patch.

In FIGS. 16 and 17, since a thick arrow indicates a carrying directionof a print paper, printing is performed from the lower side toward theupper side of the print paper. Therefore, an RGB value at the lower edgeof each of the print patches is first printed.

Each of the print patches is disposed in the order of an RGV value fromsmall to large because printing is performed from a patch whose inkvolume for printing is larger to a patch whose ink volume for printingis smaller.

The present inventor and others have studied and found out that whenprinting is performed using “a long head” as illustrated in FIG. 1, ontop of an uneven color caused by manufacturing variations, an uneven inkdensity tends to occur in which a density varies at a start position ofprinting of an image to a main scanning direction. Specifically, whenprinting attempts to be started after an array of ejection ports has notejected ink due to a blank space of an image and so on for apredetermined time period during printing, an ink density adjacent tothe ejection ports increases due to evaporation of ink from a surface ofthe ejection ports. This may cause an uneven ink density that makes thestart position of printing of an image dense.

FIG. 18 is a diagram illustrating a relationship between the number ofejection for each ejection port and an ink density ratio. The inkdensity ratio is defined by an ink density increased from a normal inkdensity due to evaporation. Since ink evaporates from a surface of anejection port, how many ejected ink droplets from the first ink droplethave an increased density varies depending on the degree of evaporation.Three polygonal lines indicate a case in which the first ejected inkdroplet has an increased density, a case in which the first and secondink droplets have an increased density, and a case in which the first,second and third ink droplets have an increased density, respectively.If dots with an increased ink density are concentrated in a startposition of printing of an image in this way, an uneven ink density canvisually be recognized.

As the number of print patches increases, the possibility of occurrenceof the aforementioned uneven ink density increases while the patches arebeing printed. This possibility can be reduced by printing a patch inthe order of an ink volume for printing from large to small due to thefollowing reasons.

Since, in a patch with a larger ink volume for printing, ink is ejectedfrom each ejection port twice or three times with the smaller number ofpixels, an effect of an uneven ink density is limited to a narrow space.As the result, an uneven ink density of this has a smaller effect than apatch with a smaller ink for printing.

While a patch with a larger ink volume for printing is being printed, afrequency of ejection is high and therefore an uneven ink density isunlikely to occur when the next patch in printed.

In FIGS. 16 and 17, patches are arranged in the order of an RGB valuefrom small to large because in this arrangement patches are arranged inthe order of an ink volume to be used from large to small. A suitablearrangement may vary depending on a type of ink to be used and how touse the ink. In the following case, an ink volume to be used for a cyanpatch may be larger than an ink volume to be used for a blue patchdepending on how to use a light cyan. For example, it applies to thecase where a light cyan ink as well as CMYK four colors are used toperform printing and the case where patches of cyan (0, 255, 255) toblue (0, 0, 255) colors are arranged.

In such a case, in the order of an RGB value from large to small,printing a cyan patch first reduces the possibility of occurrence of anuneven ink density.

Alternatively, an arrangement of patches may be decided depending on anink volume for printing that is more affected by the uneven ink density,instead of an ink volume for printing of all inks of the patches.

In the case where the number of ink colors for printing the patches ismore or equal to three, patches that need the more number of ink colorswith a larger ink volume may be first printed.

First Variation of First Embodiment

FIG. 4B is a block diagram illustrating a configuration of an imageprocessing unit of an inkjet printer according to a first variation. InFIG. 4B, sections indicated by reference characters 401 and 405 to 409are identical to sections indicated by the same reference characters inFIG. 4A, and therefore will not be described. This variation isdifferent from the configuration illustrated in FIG. 4A in that an inputcolor conversion processing section and an MCS processing section areintegrated as one processing section.

Specifically, an input color conversion processing & MCS processingsection 411 uses one table generated by combining a table of the inputcolor conversion processing section and a table of the MCS processingsection. This allows for color shift correction processing directly onimage data inputted from the input unit 401, thereby outputting devicecolor image data whose color shift has been reduced.

FIGS. 20A and 20B are flow charts, illustrating processing to generatetable parameters for the MCS processing section and processing by theMCS processing section, respectively, according to the first variation,which are similar to those in FIGS. 5A and 5B. Processing S910 togenerate table parameters for the MCS processing section in FIG. 20A isdifferent from the processing S510 in FIG. 5A with respect to processingof Step S902 and Step S906. The processing in Step S902 and S906 will bedescribed below.

In Step S902, an image for measurement is printed on a print paper forcolor shift correction, on the basis of color image data I[X] inputtedfrom the input unit 401. In doing so, of the input color conversionprocessing & MCS processing section 411, only a portion corresponding tothe input color conversion processing section is made to function, andthe MCS processing is skipped through a bypass processing path indicatedby the dash line 410. Specifically, the input color conversionprocessing & MCS processing section 411 is configured to be able to usetwo tables by switching. That is, for input image data I[X], a tablehaving color conversion W′ that is combination of the input colorconversion processing and the processing of the MCS processing section,which will be described below, as table parameters and a table havingtable parameters of only the input color conversion processing areswitched to be used. In printing an image for measurement, the table ofonly the input color conversion processing is used by switching.

A color conversion coefficient of input color conversion processing withthis table used for printing an image for measurement is set to be ainput color conversion W, then, the following expression is established:device color data D[X]=input color conversion W (input image data I[X]).Uniform device color image data D[X] obtained in this way, as with thefirst embodiment, proceeds through the ink color conversion processingsection 405, HS processing section 406, TRC processing section 407 andquantization processing section 408 to the output unit 409, where thedata is printed on the print paper 106 as an image for measurement.

In Step S906, an equivalent color conversion W′[X] as a table parameteris calculated from a correction value T⁻¹[X] for each area. This W′[X]is color conversion that combines the input color conversion W andequivalent color correction Z⁻¹[X]. Calculation processing of theequivalent color correction Z⁻¹[X] is the same as that of the firstembodiment and therefore will not be described.

In processing S920 in FIG. 10B, which is processing by the input colorconversion processing & MCS processing section 411 in generating printdata, the equivalent color conversion W′[X] generated as above as atable parameter is used to correct a color shift. That is, color shiftcorrection is performed on input color image data I[X] corresponding toeach area, and device color image data D′[X] that has been subjected tocolor shift correction is outputted. Then, the device color image dataD′[X] is subjected to processing in the ink color conversion processingsection 405 and the subsequent sections, and printed on the print paperis the output unit 409.

According to the aforementioned variation, since equivalent colorconversion W′[X] is set in Step S906 so that device color image dataD′[X] has the same value as that of the first embodiment, a color shiftcan be reduced, as with the first embodiment. Since combined colorconversion W⁻¹[X] of equivalent color correction Z⁻¹[X] and input colorconversion W is stored as one three-dimensional lookup table, the numberof times to refer to the lookup table can be reduced from twice to oncein generating print data in comparison with the first embodiment,thereby improving a processing speed. Meanwhile, the first embodimenthas an advantage over the first variation in the following point. Thatis, in the first variation, three-dimensional lookup tablescorresponding to “the number of print regions” and “types of inputcolors” must be stored, and therefore the number of three-dimensionallookup tables to be stored increases in proportion to increase of typesof input colors (for example, sRGB, YCC, L*a*b*). In the firstembodiment, the number of three-dimensional lookup tables to be storeddoes not increase even if types of ink colors increase. It can be saidthat in the first variation a correction accuracy is reduced due tocombining lookup tables.

Second Variation of First Embodiment

FIG. 4C is a block diagram illustrating a configuration of an imageprocessing unit according to a second variation of the first embodiment.As illustrated in FIG. 4C, in the present variation, processing by theMCS processing section 404 is performed before processing by the inputcolor conversion processing section 403.

FIGS. 13A and 13B are flow charts, illustrating processing to generatetable parameters for the MCS processing section and processing by theMCS processing section, according to the second variation, respectively,which illustrate the similar processing illustrated in FIGS. 5A and 5B.In processing S1010 in FIG. 13A, processing in Steps S1002 and S1006 isdifferent from processing in FIG. 5A, which will be described below.

In Step S1002, input color image data I[X] from the input unit 401bypasses the MCS processing section 404 to the input color conversionprocessing section 403, where the input color image data I[X] isconverted to device color D[X]. After that, as with FIG. 5A according tothe first embodiment, the device color D[X] proceeds through the inkcolor conversion processing section 405, HS processing section 406, TRCprocessing section 407 and quantization processing section 408 to theoutput unit 409, where an image for measurement is printed on the printpaper 106. Then, in Step S1006, an equivalent correction value Y⁻¹[X] tocorrect a color of an input color space is calculated.

The equivalent correction value Y⁻¹[X] is a correction value to correctan input color equivalent to an equivalent correction value Z⁻¹[X] thatcorrects a color of a device color space that is calculated in Step S506of FIG. 5A. The calculation processing of the equivalent correctionvalue Y⁻¹[X] is the same as that of the first embodiment and thereforewill not be described here.

Next, the procedure of processing S1020 in FIG. 13B are as follows. InFIG. 13B, in Step S1007, the MCS processing section 404 corrects inputcolor image data I[X] for each area in such a way that an equivalentcorrection value Y⁻¹[X] is applied to the input color image data I[X]for each area, using the table generated in the processing S1010. Thenin Step S1008, input color image data I′[X] corrected by the equivalentcorrection value Y⁻¹[X] is converted to device color image data D′[X] inthe input color conversion processing section 405. Processing subsequentto this processing is the same as that of the first embodiment andtherefore will not be described here.

According to the present variation, processing by the MCS processingsection 404 is performed before processing by the input color conversionprocessing section 403, thereby improving independence of modules. Forexample, the present variation can be applied, as an expanded function,to an image processing unit without an MCS processing section. Or, theprocessing can be performed in the host PC.

Third Variation of First Embodiment

FIG. 4D is a block diagram illustrating a configuration of an imageprocessing unit according to a third variation of the first embodiment.As illustrated in FIG. 4D, the present variation relates to aconfiguration without the HS processing section 406 illustrated in FIG.4A.

Processing to generate table parameters for the MCS processing sectionand processing by the MCS processing section in the present variationare the same as processing illustrated in FIGS. 5A and 5B according tothe first embodiment except that head shading is not performed in the HSprocessing section in the present variation. That is, HS processing isnot performed before Step S502 illustrated in FIG. 5A.

FIGS. 11A and 11B are diagrams illustrating printing examples of animage for measurement in Step S502 of FIG. 5A according to the presentvariation, which are similar to the diagrams illustrated in FIGS. 6A and6B. As illustrated in FIG. 11B, since HS processing is not performed inprinting of an image for measurement, the number of printed dots is thesame between a region corresponding to four nozzles on the left in theFIG. 11B and a region corresponding to four nozzles on the right in theFIG. 11B. As a result, the color of the region on the right has astronger magenta cast in comparison with the example illustrated in FIG.6B according to the first embodiment. As a result, in generating tableparameters in processing S510 illustrated FIG. 5A, a correction value toreduce magenta color is generated. This enables a correction value forobtaining an printing result illustrated in FIG. 7B to be a tableparameter for the MCS processing, thereby reducing a color shift withoutperforming HS processing.

In addition, direct advantageous effects of not performing HS processinginclude: the increase of a processing speed, the reduction of resourcessuch as a table for HS processing, the reduction of processing processesby not performing “printing”, “measurement” or “correction parametergeneration” for HS processing. Meanwhile, the first embodiment has anadvantage over the third variation in the following point. That is, inthe third variation, since MCS processing corrects both a single inkcolor gradation and an uneven color due to variations of an ejectionvolume, if a three-dimensional lookup table having the same size as thatof the first embodiment is used, a correction accuracy is reduced. Inorder to realize the same correction accuracy as that of the firstembodiment, a measure such as the increase of a size of the lookup tableneeds to be taken. It can be said that in the first embodiment since ansingle ink color gradation is to be corrected by HS processing and anuneven color is corrected by MCS processing, a correction accuracy ishigh.

The first embodiment and the first to third variations thereof have beendescribed. The content of processing is only an example, but any meanscan be used as long as the means can realize the reduction of an unevencolor that is an effect of the present invention.

For example, in the processing to generate parameters for MCS processingin FIGS. 5A, 9A and 10A, a method in which a color shift amount is firstmeasured and then a correction value is calculated is used. However,other methods can be used.

Since an objective of the present invention is to reduce an unevencolor, setting a target color A is not essential. That is, a correctionvalue for each print region may be set on the basis of a color shiftbetween the print regions.

In FIG. 2, a region corresponding to four nozzles is set to one printregion, but the present embodiment is not limited to this. A regioncorresponding to more than four nozzles may be set to one print regionor a region corresponding to less than four nozzles, such as one nozzle,may be set to one print region. The number of nozzles belonging to eachprint region is not necessarily the same, but can be properly setdepending on a property of a device.

Second Embodiment

FIG. 19A is a block diagram illustrating a configuration of an imageprocessing unit to generate print data according to a second embodimentof the present invention. The configuration illustrated in FIG. 19A isdifferent from the configuration according to the first embodimentillustrated in FIG. 4A with respect to processing by an ink colorconversion processing & MCS processing section 2104. The processing bythis ink color conversion processing & MCS processing section 2104 willbe described below.

The ink color conversion processing & MCS processing section 2104performs ink color data conversion processing as well as colorcorrection processing on device color image data obtained by input colorconversion processing thereby to output ink color data whose color shifthas been reduced.

FIGS. 20A and 20B are flow charts illustrating processing to generateparameters of a table to be used by the ink color conversion processing& MCS processing section 2104 illustrated in FIG. 19A and processing bythe ink color conversion processing & MCS processing section 2104 usingthe table, respectively.

In FIGS. 20A and 20B, processing in Steps S2306, S2307 and S2308 isessentially different from the processing according to the firstembodiment illustrated in FIGS. 5A and 5B, and which will be describedbelow.

In Step S2306 of FIG. 20A, an ink color conversion & MCS processingparameter G′[X] is calculated from a correction value T⁻¹[X] for eacharea. This calculation processing are roughly divided to two processing:processing to calculate an equivalent correction value Z⁻¹[X] from acorrection value T⁻¹[X] and processing to calculate an ink colorconversion & MCS processing parameter G′[X] from the equivalentcorrection value Z⁻¹[X].

First, an equivalent correction value Z⁻¹[X] is calculated from acorrection value T⁻¹[X]. If the correction value T⁻¹[X] is a correctionvalue of a blue color in a measurement color space, an equivalentcorrection value Z⁻¹[X] to correct a blue color of a device color spaceby the same amount of this correction value T⁻¹[X] in a device colorspace is calculated on the basis of this correction value.

Here, an equivalent correction value Z⁻¹[1] is an equivalent correctionvalue in a region corresponding to four nozzles in FIG. 6B and isideally zero. Meanwhile, an equivalent correction value Z⁻¹[2] is anequivalent correction value on the right in FIG. 6B and is a correctionvalue to reduce a cyan color.

If a measurement color space is identical to a device color space, thefollowing expression is established as with the first embodiment:

Z ⁻¹[1]=T ⁻¹[1]=−T[1]=A−B[1]=(Rt−R1,Gt−G1,Bt−B1)

Z ⁻¹[2]=T ⁻¹[2]=−T[2]=A−B[2]=(Rt−R2,Gt−G2,Bt−B2)

However, in many cases, they are not identical to each other. In suchcases, color space conversion is necessary.

If linear conversion can be performed between the both color spaces, aknown method such as matrix conversion described in the first embodimentcan be used. If linear conversion cannot be performed between the bothcolor spaces, a known method such as a three-dimensional lookup tablecan be used, as described in the first embodiment.

If the relationship between a correction value T⁻¹[X] and an equivalentcorrection value Z⁻¹[X] varies depending on a color, the equivalentcorrection value Z⁻¹[X] can be obtained as described in the firstembodiment as follows:

Z ⁻¹[1]=F(Rt,Gt,Bt)−F(R1,G1,B1)

Z ⁻¹[2]=F(Rt,Gt,Bt)−F(R2,G2,B2)

In this case, next, a table parameter G′[X] of ink color conversion &MCS processing is obtained from the equivalent correction value Z⁻¹[X]as follows. F (Rt, Gt, Bt) is set to device color information D[X] (dR,dG, dB) that is inputted to the ink color conversion processing & MCSprocessing section 2104 illustrated in FIG. 20A in printing an image formeasurement. In this case, the following expression is established:

Z ⁻¹[1]=(dR,dG,dB)−F(R1,G1,B1)

Z ⁻¹[2]=(dR,dG,dB)−F(R2,G2,B2)

Next, corrected ink color information C′ [X], which is obtained in sucha way that an equivalent correction value is applied to inputted devicecolor information D[X], then which is subjected to ink color conversionprocessing G, is found as follows:

C′[1]=G((dR,dG,dB)×2−F(R1,G1,B1))

C′[2]=G((dR,dG,dB)×2−F(R2,G2,B2))

where corrected ink color information C′[1] corresponds to a region onthe left in FIG. 7B and is ideally equivalent to G (dR, dG, dB).Meanwhile, corrected ink color information C′[2] corresponds to a regionon the right in FIG. 7B and whose cyan color component has been reduced.

Lastly, a parameter G′[X] of ink color conversion & MCS processing isdecided so as to convert input device color data D[X] to corrected inkcolor information C′[X] as follows:

G′[1](dR,dG,dB)=C′[1]

G′[2](dR,dG,dB)=C′[2]

As described above, in ink color conversion & MCS processing parametergeneration processing S2310 illustrated in FIG. 20A, a table parameterG′[X] for the ink color conversion & MCS processing section can begenerated for each area. Then, this table parameter G′[X] for the inkcolor conversion & MCS processing for each area is stored in the HDD 303of the host PC.

Next, correction processing S2320 by the ink color conversion & MCSprocessing section illustrated in FIG. 20B will be described.

In Step S2307 of FIG. 20B, first, the parameter G′[X] of ink colorconversion & MCS processing generated in the processing S2310 is appliedto device color image data D[X] for each pixel corresponding to thearea, thereby performing correction.

Specifically, which area includes a pixel of interest to be subjected toimage processing is first decided to obtain a print region number n ofthe area including the pixel of interest. Suppose that the n-th area isan area of interest. An equivalent correction value Z⁻¹[n] associatedwith this area of interest is obtained by selecting from equivalentcorrection values stored in the HDD 303 of the host PC. Then, theparameter G′[X] of ink color conversion & MCS processing is applied tothe device color image data of the pixel of interest as follows. Thatis, processing in the ink color conversion & MCS processing section 2104applies the parameter G′[X] to the device color image data D[X] therebyto generate corrected ink color data C′[X].

C′[1]=G((dR,dG,dB)×2−F(R1,G1,B1))

C′[2]=G((dR,dG,dB)×2−F(R2,G2,B2))

where the corrected ink color data C′[1] corresponds to a region on theleft in FIG. 7B and is ideally the same blue color as the target colorA. The corrected ink color data C′[2] corresponds to a region on theright in FIG. 7B and is a blue color whose cyan color has been reduced.

Next, in Step S2308 of FIG. 20B, corrected ink color data goes throughan HS processing section 2106, a TRC processing section 2107 and aquantization processing section 2108 to an output unit 2109, where thedata is printed on the print paper 106.

As described in FIGS. 7A and 7B, since in each print region of the printpaper 106, a color shift amount T[X] occurs due to variations ofejection volumes during printing, the following relationships areobserved:

Color information on the left in the print paper≈a color of print papercorresponding to C′[1]+T[1]≈A

Color information on the right in the print paper≈a color of print papercorresponding to C′[2]+T[2]≈A

where C′[1] is ideally the same blue color as the target color A andT[1] is ideally zero; and C′[2] is a blue color whose cyan color hasbeen reduced by T[2] relative to the target color A, where T[2] is ashift amount to increase a cyan color. In this way, the blue color onthe left and the blue color on the right in the print region becomeapproximately the same, thereby reducing an uneven color.

As another example of MCS processing parameter generation processing2310, the method described with reference to FIG. 8 may be used.

First Variation of Second Embodiment

The present variation relates to a mode corresponding to the firstvariation of the first embodiment. FIG. 19B is a block diagramillustrating an image processing configuration in which input colorconversion processing and ink color conversion processing & MCSprocessing are integrated, according to the present variation. Thisvariation also can increase a processing speed as with the firstvariation of the first embodiment.

Second Variation of Second Embodiment

The present variation relates to a mode corresponding to the thirdvariation of the first embodiment. FIG. 19C is a block diagramillustrating an image processing configuration without HS processing,according to the present variation.

Processing according to the present variation is the same as processingillustrated in FIGS. 5A and 5B except that in the present variation HSprocessing is not performed, as described in the third variation of thefirst embodiment.

In the aforementioned embodiments, a first color signal can be a colorsignal in a color space of any of RGB, Lab, Luv, LCbCr and LCH that doesnot depend on a print head, and a second color signal can be a colorsignal in a color space that depends on a color of ink ejected by aprint head.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2010-118673, filed May 24, 2010, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A data processing apparatus performing colorcorrection processing on a color signal of each pixel of image data tobe printed on a print medium using a print head, the color signal havinga plurality of elements in a predetermined color space, the dataprocessing apparatus comprising: a table generation unit configured togenerate a plurality of correction tables assigned to each nozzle oreach of a predetermined number of nozzles that are used for printing ona common region in the print medium in a plurality of nozzle arrays,respectively, the plurality of nozzle arrays being formed on the printhead and ejecting a plurality of inks including a first ink and a secondink having a different color from the first ink, wherein the tablegeneration unit generates each of the plurality of correction tables onthe basis of an ink ejection property of nozzles that eject at least thefirst and second inks.
 2. The data processing apparatus according toclaim 1, further comprising a pattern generation unit configured togenerate a pattern on a print medium with the use of the print head, thepattern being used to generate each of the plurality of correctiontables.
 3. The data processing apparatus according to claim 1, whereineach of the plurality of correction tables has a color cube of colorsignals, each of the color signal having three elements, the patterngeneration unit generates a pattern of a color signal corresponding to agrid point of each edge of the color cube on a print medium with the useof the print head, and the table generation unit has a interpolationunit that uses color information obtained from the each pattern tointerpolate grid points on a surface and inside the color cube.
 4. Thedata processing apparatus according to claim 3, wherein the patterngeneration unit forms a pattern of a color signal with the use of theprint head, the color signal corresponding to at least either of a gridpoint on which the three elements are equal and a grid point on whichtwo of the three elements are equal and remaining one element is aminimum or maximum value, in addition to the grid point on each edge ofthe color cube.
 5. The data processing apparatus according to claim 2,wherein the correction table has a color cube of color signals, each ofthe color signal having three elements, and the pattern generation unitgenerates a pattern of a color corresponding to a grid point of eachedge of the color cube on a print medium with the use of the print headin the order of a value of the three elements from small to large. 6.The data processing apparatus according to claim 2, wherein thecorrection table has a color cube of color signals, each of the colorsignals having three elements, and the pattern generation unit generatesa pattern of a color signal corresponding to a grid point of each edgeof the color cube on a print medium with the use of the print head inthe order of an ink ejection volume from large to small.
 7. The dataprocessing apparatus according to claim 1, wherein a color signal beforethe color correction processing is a color signal in a color space ofany of RGB, Lab, Luv, LCbCr, and LCH that does not depend on the printhead, and a color signal after the color correction processing is acolor signal in a color space that depends on a color of ink ejected bythe print head.
 8. The data processing apparatus according to claim 1,wherein a color signal before the color correction processing is a colorsignal in a color space of any of RGB, Lab, Luv, LCbCr, and LCH thatdoes not depend on a color of ink ejected by the print head, a colorsignal after the color correction processing is a color signal in thesame color space as the color space of the color signal before the colorcorrection processing, and the correction table is used to convert acolor signal before the color correction processing to a color signal ina color space that depends on a color of ink ejected by the print head.9. The data processing apparatus according to claim 1, wherein a colorsignal before and after the color correction processing is a colorsignal in a color space that depends on a color space of ink ejected bythe print head.
 10. A data processing method for performing colorcorrection processing on a color signal having a plurality of elementsin a predetermined color space, each pixel of image data to be printedon a print medium with the use of a print head having the color signal,the data processing method comprising: generating a plurality ofcorrection tables assigned to each nozzle or each of a predeterminednumber of nozzles that are used for printing on a common region in theprint medium in a plurality of nozzle arrays, respectively, theplurality of nozzle arrays being formed on the print head and ejecting aplurality of inks including a first ink and a second ink having adifferent color from the first ink; and generating each of the pluralityof correction tables on the basis of an ink ejection property of anozzle ejecting at least the first and second inks.